Leveraging Bicep deployer for Automated RBAC Assignments

Hello Folks,

Today, I'll go through a topic that I believe is a real time-saver—one that keeps automation running smoothly and ensures it's effectively integrated into bicep templates. In this article, I'll share my experience with the Bicep deployer() function. I’ll explain how it streamlines the process of provisioning resources like Azure Key Vaults while automating RBAC-based access.

What Is the deployer Function?

The deployer() function in Bicep returns details about the identity executing the deployment. Essentially, it tells you which service principal or managed identity is running your deployment. I find this incredibly useful because it allows me to reference the deployer’s identity directly in my templates—ensuring that the correct permissions are automatically applied without hardcoding any object IDs for the deployments.

Example output of the deployer() function looks like this:

{
  "objectId": "12345678-1234-1234-1234-123456789abc",
  "tenantId": "87654321-4321-4321-4321-cba987654321"
}

Why I Use deployer

When provisioning resources like an Azure Key Vault, it's crucial to grant specific permissions to the identity executing the deployment. By using deployer(), I can dynamically retrieve the deploying identity and assign the necessary RBAC roles without manual intervention or unnecessary inputs. This is particularly valuable when running deployments through pipelines like Azure DevOps or GitHub Actions, where you can avoid hardcoding the service principal object ID as a parameter. Instead of requiring manual intervention to supply the deployment service principal's object ID, deployer() automatically retrieves it during runtime, streamlining the process and reducing the potential for human error, dependency on external scripts or inputs.

By leveraging deployer(), I can automatically assign the necessary RBAC roles to the deploying identity. For example, after setting up a Key Vault, I can ensure that the deployer is granted the Key Vault Contributor role. This is essential for managing secrets, certificates, and other sensitive information without any extra manual configuration.

Simplified Automation

Automation is key in modern deployments. Embedding access control directly into the Bicep template using deployer() means there's no need for additional scripts or manual adjustments. This makes my deployment pipelines more robust and less prone to errors.

I typically use deployer() in scenarios where the deployment involves provisioning sensitive resources that require strict access controls. For instance, when deploying an Azure Key Vault, rather than managing service principal objectId's separately, I let deployer() dynamically assign the appropriate RBAC permissions to the identity running the deployment. This not only simplifies the deployment process but also enhances security by ensuring that only the necessary permissions are granted to the deploying identity.

Provisioning a Key Vault with deployer() and RBAC

Below is a Bicep template that demonstrates how I deploy an Azure Key Vault and assign the deployer’s identity the Key Vault Contributor role:

// Define the resource group scope
targetScope = 'resourceGroup'

// Parameter for the Key Vault name
param keyVaultName string = 'myKeyVault'

// Provision the Key Vault
resource keyVault 'Microsoft.KeyVault/vaults@2022-07-01' = {
  name: keyVaultName
  location: resourceGroup().location
  properties: {
    tenantId: subscription().tenantId
    sku: {
      family: 'A'
      name: 'standard'
    }
    accessPolicies: [] // Access policies will be managed through RBAC
  }
}

// Assign the Key Vault Contributor role to the deployer (service principal/managed identity)
resource deployerRoleAssignment 'Microsoft.Authorization/roleAssignments@2020-04-01-preview' = {
  name: guid(keyVault.id, deployer().objectId, 'KeyVaultContributor')
  properties: {
    roleDefinitionId: subscriptionResourceId('Microsoft.Authorization/roleDefinitions', 'b86a8fe4-44ce-4948-aee5-eccb2c155cd7') // Key Vault Contributor role
    principalId: deployer().objectId
    principalType: 'ServicePrincipal'
    scope: keyVault.id
  }
}

What This Template Does:

• Key Vault Deployment: The template creates an Azure Key Vault without preset access policies, ensuring that all access is managed via RBAC.
• Role Assignment: By using deployer().objectId, the template dynamically retrieves the identity executing the deployment and assigns it the Key Vault Contributor role. This guarantees that the deployer has the necessary permissions to manage the Key Vault post-deployment.

Best Practices from my experience

• Follow the Principle of Least Privilege: Always grant only the permissions that are necessary. In this case, the Key Vault Contributor role is sufficient for managing the Key Vault without exposing broader access.
• Embrace Dynamic Deployments: With deployer(), my templates become much more adaptable. This is especially useful when different environments or service principals are used, eliminating the need for environment-specific adjustments.

Conclusion

The Bicep deployer() function has transformed how I handle secure deployments, particularly when managing sensitive resources like Azure Key Vaults. By dynamically referencing the deployer’s identity, I can streamline access control, enhance security, and simplify the overall deployment process. I hope this example inspires you to explore dynamic identity management in your own Bicep templates and enjoy the benefits of a more automated, secure deployment process.

Stay tuned for more insights and practical examples in my upcoming articles. Happy deploying!